WASSERBAU-STAUGEWAESSER

For centuries, water has been stored or transported in manmade canals
and reservoirs to make it usable for transportation, as a source of
energy, or for irrigation. A wide range of geosynthetic products can be
used in order to create more efficient shipping routes, including those
used for the construction or repair of canals and docks. Geosynthetics
facilitate economical and ecological methods for the construction of
retention reservoirs or barrages.

Filtration

When used for transportation hydraulic engineering, Terrafix®
needle-punched nonwoven geotextiles can be used effectively below
permeable revetments as a filter layer. They are selected and designed
in accordance with the established technical guideline “Instructions for
the use of geotextile filters in waterways” (MAG) of the Federal
Institute of Hydraulic Engineering (BAW, Karlsruhe, Germany, 1993).
Depending on the existing soil type and revetment, Terrafix® nonwoven
geotextiles that are at least 4.5 mm to 6.0 mm thick are best suited to
prevent erosion and soil displacement (please refer to chapter
“Filtration”). Even under high hydrodynamic loads caused by rapid water
level fluctuations or by the turbulence from ship propellers, Terrafix®
nonwoven geotextiles maintain their mechanical properties and filter
efficiency. Composite Terrafix® products which exhibit a coarse fibre
layer can be effectively employed to stabilise the soil/filter boundary
layer in soils with high single grain mobility, preventing particle
displacement under the Terrafix® filter geotextile.

High mechanical stresses can occur during the installation process as
well as from ship traffic. For this reason, the geotextile filters must
exhibit adequate impact and abrasion resistance. Terrafix® geotextiles
offer these properties and more! Their high elongation capacity and
robustness allow them to easily accommodate irregular or soft subgrades
while preventing damage to the nonwoven structure itself when covered
with stone. The three-dimensional needle-punched structure of crimped
fibres provides high abrasion characteristics and resistance to any
movement of the revetment.

In fast flowing or turbulent waters caused by propeller wash, the
general physical characteristics make the installation and positioning
of a nonwoven geotextile an inexact science. However, the Terrafix® sand
mat enables the filter geotextile to be placed quickly and accurately
underwater due to the ballast of an encapsulated sand mass, providing
simple permanent stability. Terrafix® offers filter stability against
finely grained soils while sufficiently robust to resist damage from
stone cover.

Sealing

In inland fresh water shipping routes where the water level is at an
elevation higher than the natural groundwater level, artificial sealing
is required to prevent the water from “draining” to the groundwater
level. Bentofix® geosynthetic clay liners or Carbofol® geomembranes are
well suited lining products for dry installations. When using
geomembranes, Terrafix® or Secutex® needle-punched nonwoven geotextiles
are recommended as a protective layer. Structured or textured Carbofol®
geomembranes are available to effectively transfer shear forces on
challenging slope designs. Regardless, projectspecific direct shear
tests should be performed to verify the required shear strength
parameters in order to use them for calculating slope stability
analysis.

When inland ship traffic cannot be interrupted, the underwater
installation of Bentofix® BZ 13-B geosynthetic clay liner is
recommended. It features a bentonite clay liner with an additional sand
ballast layer and an encapsulating nonwoven geotextile. Due to our
unique technology, this geotextile/liner composite is uniformly
reinforced with direction-independent needle punching over its entire
surface area. With a mass per unit area of 8 kg/m², the heavy, sand fill
performs several functions: it facilitates the uniform swelling of the
bentonite which ensures consistent hydraulic function throughout the
entire GCL; it protects against impact stress during the installation of
covering stones; and with the appropriate installation technology, it
ensures precise positioning so that the Bentofix® BZ 13-B clay liner and
sand ballast remain in a permanent, stable position even during
shipping traffic. Bentofix® BZ 13-B is also uniformly impregnated with
bentonite powder over its entire edge surface area to ensure the proper
sealing performance in the overlaps.

Protection

Depending on the subgrade and the cover material, properly specified
needle-punched protective nonwoven geotextiles such as Terrafix® or
Secutex® both above and below the Carbofol® geomembrane will minimise
the potential for damage from surrounding soils. For slightly
gravely-sand (≤ 30 % gravel portion) or corresponding cover material, a
needlepunched nonwoven geotextile with a mass per unit area of 400 g/m²
should be used. Coarser grained soils may require nonwovens exhibiting a
mass per unit area of at least 1,200 g/m².

Erosion control

On slopes with especially fine grained soils, heavy precipitation and
wave impact may cause surface erosion. Significant erosion and rutting
can occur if the slope is poorly vegeta ted. Geosynthetic erosion
control mats are commonly used to address difficult, erosion-prone slope
conditions. Secumat® erosion control mat can significantly reduce soil
washout during heavy rainfalls – its three-dimensional, irregular
labyrinth-like structure is designed to allow both fine grained and
gravelly soils to fill the open convoluted structure. The irregular
Secumat® structure holds the soil in position on steeper slopes and
provides structural support to vegetation during the early stages of
plant growth. The use of high quality propylene (PP) resins make
Secumat® resistant to naturally occurring soil chemicals, soil
microorganisms and UVradiation. The Secumat® product range is also
available with a needle-punched nonwoven geotextile attached to the
bottom side. Installed with the three-dimensional mesh surface side-up,
it will then perform two functions – soil separation as well as erosion
control.

Conclusion

Robust Terrafix® geotextiles can be effectively employed under
permeable revetments to provide filter stability to the subsoil.
Bentofix® geosynthetic clay liners and Carbofol® geomembranes are ideal
products for a myriad of sealing applications. Carbofol® must be
installed under dry conditions and is protected against mechanical loads
by Terrafix® or Secutex® nonwoven geotextiles. Conversely, Bentofix®
can be installed under water – the integrated sand mat provides a
controlling confining load during the swelling of the bentonite and
protects the bentonite mat when it is covered with cover stones. In
areas where wave impact occurs, Secumat® protects slopes from erosion
during the early stages of plant growth.